1. Field
An aspect of the present invention relates to a printed wiring board having a land and an electronic apparatus having the printed wiring board.
2. Description of the Related Art
For example, a printed wiring board in which a land for grounding is provided around a fixing hole for bolting the printed wiring board is disclosed. This printed wiring board comprises a substrate, a fixing hole provided to penetrate through the substrate, a land provided in doughnut shaped around the fixing hole in a surface of the substrate, and a solder cream printed on the surface of the land.
In printed wiring boards of this type, usually, the surfaces of the lands are subjected to solder plating to prevent corrosion of the lands and attain reliable grounding. A printed wiring board having a cost advantage over ones in which the lands are subjected to solder plating is provided by supplying solder also to the land surfaces when cream solder is supplied to mounting patterns of other components (see JP-A-2000-244080, for instance).
In recent years, with the increase in miniaturization and functionality of digital equipment, the high-density mounting on a printed wiring board and the securing of a wide mounting area have come to be required increasingly. However, the above donut-shaped lands raise a problem that the mounting area on the printed wiring board is reduced by areas corresponding to the spaces for formation of the lands. For another thing, to secure a wide mounting area on a printed wiring board, it is effective to locate the fixing holes as close to the outer periphery of the board as possible. However, in the printed wiring boards, the fixing holes cannot be located sufficiently close to the outer periphery because margins for formation of the donut-shaped lands need to be secured around the respective fixing holes.
Each of these margins needs to be set taking into consideration not only the space for formation of the land but also a variation that may occur when a land pattern is formed by etching. This is because if a land is formed in contact with the periphery the land is exposed in an end face of the printed wiring board, as a result of which the printed wiring board may be short-circuited with another component. This also requires sufficient margins around the respective fixing holes.
On the other hand, one method for reducing the above margins is to narrow the widths of the donut-shaped lands. However, if the land widths are narrowed, a land pattern may be disconnected due to a variation in forming the pattern. Furthermore, since the lands are reduced in strength, the land patterns are prone to peel off when bolting is performed through the fixing holes. Further, since the land is a part for grounding on the casing, a contact area between the land and the bolt is narrowed if the width of the land is made smaller, possibly resulting in the lower reliability of the grounding.
For the above reasons, the printed wiring boards cannot sufficiently satisfy the recent requirements of high-density mounting and securing of a wider mounting area.